


Using Logic on Shonen Superpowers is Inadvisable At Best

by Moraith



Category: Dr. STONE (Manga), Jump Force
Genre: Comedy, Crossover, Gen, Multiple Crossovers, Science Experiments
Language: English
Status: In-Progress
Published: 2019-07-02
Updated: 2019-07-07
Packaged: 2020-06-02 19:26:58
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 3
Words: 5,576
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/19448014
Author URL: https://archiveofourown.org/users/Moraith/pseuds/Moraith
Summary: Senku Ishigami, nightmarish science goblin, is unleashed upon the unsuspecting members of Jump Force. He is determined to figure out a way to get something useful out of his stay in this crossover nonsense realm, so he sets himself to figuring out how all these wacky superpowers work. Unfortunately for him, he is very annoying, has no social skills, and cannot fight.One by one, with varying degrees of success, Senku unravels some of the mysteries behind the heroes of Jump Force.





	1. Test subject 1: Monkey D. Luffy

**Author's Note:**

> No one's out here writing Jump Force fanfiction, huh? That's fair.

Jump Force's second non-combat recruit was the polar opposite of Light Yagami in just about every way save for their impressive intellects. Senku Ishigami was loud, brash, and constantly in motion. He sported a tattered lab coat made of crudely-fashioned leather, dotted with stains of all sorts of strange implausible colors. The only identifiable spot on the mess was an "E = mc2" scrawled on the collar in a dark brown that any Jump Force combatant would recognize as dried blood. He had wiry unruly hair that stood straight up from his head like a living creature with its own will. His face was marred with thin lines around his eyes permanently blackened with strange necrosis, but it didn't give him any trouble. He beamed and scowled and rolled his eyes with the best of them.

Socially, Senku was something of an odd man out. Because he couldn't fight, he wasn't a member of any of the three Jump Force teams. Because he was a member of Jump Force but wasn't tied to a particular team, he flitted around the Jump Force headquarters with impunity, butting into conversations whenever he pleased and talking to anyone who caught his interest. Unlike Light, who restricted himself to the briefest possible interactions with the team leaders and otherwise kept to himself for his sanity's sake, Senku had an interest in just about everyone.

His first victim was, as it happened, one of the team leaders. It was only a day after Senku's arrival that he cornered Luffy in a hallway and asked, wide-eyed and intent,

"So, how much of you is rubber, exactly?"

Luffy blinked at him. "All of me." He hooked a finger in his mouth, then stretched his cheek out a full foot away from his teeth. "I'm a rubber man."

Senku leaned in, curiosity oozing off him in waves. "Really? Even your hair and teeth?"

Luffy let go of his cheek. It snapped back into place with a twang like a rubber band. "Who cares?" He screwed up his face. "You're nosy, huh?"

"Yup!" 

Senku began to pace, back and forth at first, then in slow circles around Luffy as he chattered. He punctuated his every word with broad dramatic hand gestures and smug self-satisfied laughter.

"You see, back home, we've lost all our rubber. A few thousand years and it all wore away! Can you believe it? We're in Japan, so we don't have any rubber trees on hand, not even in greenhouses—believe me, I've checked—and if I can bring some back, even if it's not much, I could get our electronics working better. You can do a lot without proper insulation, but can you imagine what we could do with _rubber?_ It wouldn't even have to be electronics. We need better food storage. Easy and consistent fluid transportation would be a total game changer. We'd be ten billion times better off, I'm telling you. We're using barrels right now, but we've only got a couple of people who can lug 'em around. We can't all be meatheads like Taiju, y'know? And we've only got a couple wheelbarrows and the roads are still pretty rough, so that's usually a no-go without the car anyway, and there's way too much to do to be using our only engine for _whatever_..."

Luffy tuned out everything Senku said after a sentence or two. Too complicated; not interesting. He watched Senku pace and, more specifically, watched his hair, which was just about the only thing about him worth paying attention to. Luffy pointed at the green ends of Senku's hair. 

"Why's your hair look like that?"

Senku switched tracks without missing a beat. He didn't even pause to take a breath between being interrupted and answering the question.

"Hair dye!" he announced. "It's not as long-lasting or as bright as the synthetic stuff we used to have in stores, but when your hair's naturally white like mine, it doesn't matter so much. I found some leeks growing right near where I came to, which was perfect, because I knew I could eat 'em and there were so many I had enough left over to dye my hair. Grass works too, and it's a lot easier to get your hands on, but it's way too yellow for me, so I used a bit of my food stores. Kinda risky, but ten billion percent worth it, if you ask me. I just had to boil 'em down and..."

Luffy fared no better on the paying attention front the second time around. Within seconds, his eyes were glazing over. He made the executive decision to tune Senku out and continue walking down the hall toward Sanji's kitchen for the good of all Jump Force. He was hungry.

"Wait!"

Senku's hand gripped Luffy's hair tightly. Luffy kept walking. His head stayed behind, held fast by Senku's grip, while his neck extended to allow the rest of his body to carry on. Luffy furrowed his brow at Senku while his neck stretched farther and farther down the hall. 

"You're a real pain. I'm hungry. Let go or I'll punch you."

Senku eyed Luffy's hands, which had made it most of the way down the hall. Luffy gave Senku a warning look. Down the hall, Luffy's body stopped and turned around, fist raised in a silent threat. 

Senku let go. Luffy's head flew down the hall toward the rest of his body and snapped back into place with ease. The interrogation, though, was far from over. Senku scrambled down the hall to catch up and fell into place by Luffy's side, panting from the exertion of running.

"Your hair _doesn't_ stretch!" he wheezed triumphantly. He reached for one of Luffy's hands. "What about your fingernails? Lemme see."

Luffy grimaced. "Man, you're annoying. Why's it so hard to get rid of you?"

Luffy smacked Senku, gently for Luffy, but with more than enough force to send Senku flying. Getting slammed into the wall hard enough to knock all the air out of his lungs was, thankfully, enough to shut Senku up for long enough for Luffy to make it to Sanji's kitchen in peace.

* * *

Senku came back again five courses in to Luffy's lunch. He entered the kitchen with his hands held up in surrender. Luffy glared at him through a mouthful of steak, then another one, then another one. Senku eyed Luffy's mouth with distaste, then curiosity, then shook his head and sidled over to Sanji by the stove.

Senku greeted Sanji with the same long-winded spiel about rubber and technology and yada yada yada. Luffy wouldn't have paid attention to it even if he wasn't eating. Sanji nodded along, and replied when appropriate. His hands kept moving at full speed and without the slightest error, which was good, because Luffy didn't want to have to waste any more energy on punching Senku in order to get more food. On that note, Luffy looked down at his plate and found it empty.

"Sanji!" Luffy shouted. "More food!"

"Yeah, yeah. It's coming! Hold your horses!"

A few minutes of cooking and boring conversation with the leek hair guy later, Sanji was approaching the table with another armful of plates piled high with meat. Senku stayed behind in the kitchen, leaning up against the counter and smirking to himself like he was in on some kind of scheme.

"What's with that guy?" Luffy asked, as he stretched out an arm to grab a fistful of meat from one of the plates Sanji had yet to lay on the table.

"He's a researcher. Lookin' for ways to help out his buddies back home," Sanji replied. 

When Luffy's arm came back for round two, Sanji grabbed it. He pulled a knife out of his pocket and shaved off a sliver of Luffy's fingernail. Luffy stared at Sanji, baffled, but didn't object. Sanji held up the fingernail trimming to the light and squinted at it. 

"Enjoy the food, Captain. I'll get more cooking for you in a second."

Sanji returned to the kitchen. He held out the fingernail clipping to Senku, who took it with a grin. He struggled to find a good grip on it, then discovered, much to his apparent delight, that it stretched like a rubber band. Senku asked to borrow a small corner of the stove and something to try and melt it in. Luffy shouted that he couldn't have it, reasoning that any interruption would slow down his meal. Sanji shouted, louder, that Senku was free to use anything he wanted as long as he didn't get in the way or break anything.

For lack of anything better to do, Luffy watched Senku and Sanji move around in the kitchen. Before long, Senku was leaned over a small metal pot and marveling that, "It _doesn't_ melt."

"Yeah," Sanji said, juggling his many pans filled with sizzling meats and sauces. "It's not exactly rubber. More like he's got a human body that acts like rubber. His skin burns and he bleeds when you cut him."

"That's unbelievable! What is he _made of?_ His circulatory system must be something else to keep him alive while he's ten meters long."

Sanji shrugged. "Don't ask me, kid. You're the scientist here."

Senku retreated away from the stove. He fished his test subject out of the pot and tucked it into one of his coat's many pockets, then parked himself in front of the sink and got to work on scrubbing the dishes.

"I doubt this'll be much use to me if I can't extract the rubber, but it's some exciting stuff. Given that he's still alive, I'm guessing you've got different physical laws where you're from. If I didn't have a whole world to rebuild, it'd be crazy fun to go to your world and learn it all again from the ground up. Do you even have conservation of mass? I've heard some exciting stuff about what that guy Blackbeard can do..."

Senku chattered away, mostly to himself, though Sanji occasionally came up with something to offer, while Sanji cooked and Luffy ate. Senku managed to get through washing the dishes with remarkable efficiency despite not pausing to stop talking and concentrate even once. When the sink was empty, he turned around, said a casual thanks to Sanji and strolled out of the room with a grin.

Luffy and Sanji watched him go.

"Weird guy," Luffy said.

"Weird guy," Sanji agreed.

**Notes for the Chapter:**

> Senku's notes:  
> Monkey D. Luffy's entire body has elastic properties except for his skull and his hair.  
> He says he's made of rubber, but as far as I can tell, it's just a clumsy layman's term for being stretchy. Be specific, guys!  
> Chemical composition of any part of his body: to be determined.


	2. Test subject 2: Gaara

**Notes for the Chapter:**

> Did you know that in Japan, the notation for a repeating decimal is an underline? I didn't until just now. Neat!

Team Gamma headquarters was, as usual, abuzz with activity. Gamma was the infiltration team, which meant its members didn't have the luxury of letting out all their energy in the field unrestricted like Alpha and Beta did. When they came home from information gathering, they needed an outlet for the stress and the anger and the nervous tension. It was rare for there to be a moment without a play fight or a shouting match or a ball game taking up the team's attention. 

This was one of those rare moments. This time, there was something more interesting to gawk at.

"It's the _same thing_ ," Senku insisted. 

He and Gaara stood in the main clearing, staring each other down. Gaara's arms were crossed over his chest. His neutral expression made it difficult to tell whether the gesture was defensive or dismissive. Senku was opposite Gaara, thrusting a clear crystal the size of his palm into Gaara's face.

Gaara eyed the crystal. His nose wrinkled like he had smelled something foul. 

"It is not the same thing."

"It is! It's quartz!"

Senku exhaled a sharp frustrated sigh. He tossed the quartz crystal into the air and caught it again. 

"Look, man. 'Sand' just means small rocks. The only difference is the size. You're Gaara of the desert, right? Beach sand usually has more varied mineral composition and more biologically-derived particles, but _desert_ sand is all silicates! If you can lift a hundred kilograms of that stuff..." He pointed the crystal at the sand-filled gourd on Gaara's back. "...then you should be able to lift this! The _only difference_ is that your sand has air between the stones instead of being in a single crystal structure. I know it looks different from here, but if you had it under a microscope, it would be obvious."

Gaara shook his head. He delivered his response slowly and clearly, as though he were explaining something to a small child.

"I control sand, Senku. Not crystals."

Senku retorted, with the same slow condescending tone,

"You _do_ control crystals. They're just _small._ "

Gaara pressed his lips together to stop himself from snapping at Senku. He was not, Gaara was fairly certain, being irritating on purpose. He didn't deserve to be punished for it. Gaara mustered all his patience and tried, again, to explain.

"Senku, it isn't a matter of me manipulating the physical properties of the crystals. I control _sand_. I come from a village in the desert. I learned my ninjutsu from a beast made of chakra and of _sand._ The spiritual power we draw on for our techniques doesn't follow the same rules that day-to-day technology does."

Senku mulled the explanation over. He tossed the quartz crystal again. He watched it fly, and watched the artificial sunlight beaming down from overhead shine through it. 

"...So, it's a mental block."

Gaara sighed and pinched the bridge of his nose. " _No._ "

"It's gotta be, right?" he continued. "Definitions of 'sand' vary by region and by industry anyway, so the term on its own is de facto meaningless. If you can control rocks a sixteenth of a millimeter in diameter and ones two millimeters in diameter and everything in between, it doesn't make sense that there's a cutoff above and below that."

"It doesn't matter if it makes sense," Gaara cut in. "I can demonstrate that it's impossible."

Senku flapped his free hand at Gaara dismissively. "Sure, sure. In a minute," he said. He began to pace in circles as he continued, his attention drifting away from Gaara, the sand, and the matter at hand. "...because that's just talking if you're using geological standards. That's the range scientists use. If you're really some kind of _sand whisperer_ who can only use magic on," Senku snorted and lifted his hands to make sarcastic air quotes. "' _real sand,_ ' then maybe we should find out what your size range is. It would be interesting if it didn't match up, don't you think? Maybe if we know more about what we're working with, we can figure out _why_ moving the crystal doesn't work."

Senku, having come to a decision, slipped his quartz crystal into his pocket and produced a micrometer in its place.

"Gaara, let me see the sand you _can_ control. I'm gonna measure it."

Gaara pulled a bit of sand out of his gourd and flew it over to Senku. Senku pulled one of the glass bottles off his belt. He uncorked it and held it out to Gaara, who deposited a small pile of sand inside.

"Have fun with that," Gaara said.

"I will!" Senku assured him. "Be back later."

As he shoved his way through the crowd out of Team Gamma headquarters and into the more spacious sterile work environment of the larger Jump Force complex, he held the bottle up to the light, squinting at the tiny grains in search of any visible irregularities.

* * *

Senku sprinted down the stairs to Gamma headquarters several hours later with the bottle of sand on his belt, several pages covered in dense precise handwriting in hand, and a sparkle in his eyes.

"Hey! Exciting news!" he shouted to everybody in general and nobody in particular. "You've gotta check this out!" 

Gaara chewed his mouthful of ramen thoughtfully. He would rather not, all things considered, have another conversation with Senku. Senku's increasingly insistent shouting about his findings, unfortunately, suggested that someone was going to have to bite the bullet and listen. Gaara left some money for his ramen on the counter, then stood up to approach Senku. He was the test subject, after all, so listening to Senku fell to him.

Senku didn't so much as wait for a hello before launching into a presentation of his results. He held up the papers in his hand, which were, upon closer inspection, handwritten spreadsheets filled with hundreds and hundreds of data points. 

"They're all _exactly_ the same size!" Senku announced.

He looked expectantly at Gaara, waiting for the giddy excitement to set in. It didn't. Gaara took the papers from Senku to inspect. There were hundreds of copies of the same measurement written over and over and over again, next to different ID numbers and with different increasingly excited editorial comments in the margins. Gaara flipped through all the pages of the report, looking for something to be excited about.

"...So?" Senku prompted.

Gaara looked up from the papers and met Senku's grinning face.

"This is interesting," he said, though it wasn't, particularly.

"Right?!" Senku exclaimed. He held up the bottle of sand and shook it. "You said you have an easier time controlling the sand in your gourd than other sand, right? What if this is why?"

Gaara's expression tightened. He reached out to the sand in Senku's glass bottle. It swirled and shifted at his command, just like it always did. Senku's probing, invasive though it may have been, at least hadn't changed anything.

"It's imbued with my chakra. That's why it's easier to control."

Senku planted his hands on his hips and let a smug smirk settle on his face. He leaned in toward Gaara, brandishing the bottle of swirling sand at him.

"Or is it?" he challenged. "Guess what? This isn't the sand you gave me. I made this."

Gaara balked. He let the sand in the bottle settle. Experimentally, and with great care, he set it moving again. It swirled to life with perfect ease, exactly like the sand he kept on his back. Gaara set the sand down again and met Senku's bright eager grin with astonishment. 

"You... made it? How?"

Senku pulled the quartz crystal he had been begging Gaara to manipulate earlier out of his pocket. It had been smashed into bits. Only the big chunks and the fine dust remained, the mid-sized particles having been set aside to be put in the bottle.

"Every grain of sand you gave me to look at was exactly a third of a millimeter in diameter. I got some help from Zoro over on Team Beta—which took some serious work, believe me; the dude's a pain in the ass—to grind down this quartz to the same dimensions." 

Senku put the bits of crystal back in his pocket and pulled out a second glass bottle of sand, which he held out to Gaara next to the first one. He indicated the new bottle by shaking it.

"This one is the one you gave me. The one you were controlling was mine," he explained.

He tossed both of the bottles to Gaara, who caught them in a surge of sand. 

"That's what your chakra is doing, I think. It's grinding the particles down to a uniform size. Seeing how powerful this ninjutsu stuff can be, I wouldn't be surprised if it was adding to the particles that are too small as well. You can control rock particles a third of a millimeter in diameter perfectly, but it gets harder the farther you get from that mark. That's why it only works on sand, and that's why your sand works better than the random stuff you find on the beach."

Senku beamed like the sun. Gaara considered down at the two bottles of sand, identical, but with vastly different origins.

"Do you believe I can't manipulate your crystal now?"

"You just did," Senku pointed out, smirking.

"You know what I meant."

Senku snickered and ran a hand through his hair. 

"Yeah," he said. "Just joking. Mystery solved! Isn't it exciting?! Dunno if it'll do you any good for your ninja stuff, but you _know_ now."

Gaara uncorked the bottles. He pulled the sand, Senku's and his own alike, into his gourd.

"Exciting," he agreed, with the same mild dull tone as ever. After a moment's consideration, he added, "Thanks for your interest."

Gaara held the now-empty bottles and the pages upon pages of handwritten data out to Senku, who took them eagerly.

"All in a day's work for a man of science. Leave no stone unturned! You never know what you're gonna find!"

"Dirt, usually," Gaara suggested.

Senku laughed, and nodded in assent. "Usually dirt. But hey, dirt's pretty cool, too!"

**Notes for the Chapter:**

> Senku's notes:  
> Damn, Gaara sounds _exactly_ like Athrun Zala. Kinda hot? Too bad it's not Patrick Colasour, but I'll take it.  
> Says he can control sand. Turns out he's not lying. It's size-based, not anything to do with the material. .33 mm is the size he controls best, but there's a sizable margin of error.  
> Can he control things that size that aren't rocks? This might bear further inquiry...


	3. Test subject 3: Sento Yashigami(?)

**Notes for the Chapter:**

> Dragon Ball, Naruto, and One Piece are the main features of the Jump Force multi-crossover, in that order of prominence and importance, so I figured it would only be proper to do those first, but boy oh boy, did I not have any Dragon Ball ideas. Oh, well!

Senku and Goku had been talking for hours about Saiyans and humans and the various martial arts techniques employed by the residents of Goku's universe. Goku hadn't been Senku's first choice, but Trunks never had more than a few minutes at a time to talk and Vegeta had threatened to snap his spine like a toothpick the last time Senku had tried to approach him with questions. Pointing out that his spine wasn't rigid and would snap like a _spine_ , not like a toothpick, did nothing to improve Vegeta's mood. Goku was friendlier and more patient, but he didn't have Vegeta's wits or Trunks's technical know-how. Getting useful information out of him was not unlike torture. 

Senku had his nose buried in a notebook while he talked. He had had his nose buried in his notebook for hours and he showed no signs of giving it up.

"So, anyone can do it?" Senku prompted Goku. "As long as they do the dance right?"

"As long as they're about the same height and about the same power level, yeah," Goku said. "But it's not as easy as it looks. It takes training to pull off a Fusion Dance."

Senku squinted at his notes. He scribbled something something down in the margin near the top of the page.

"How tall did you say Trunks is?"

Senku saying his son's name caught Vegeta's attention from across the clearing. He cut in with a loud derisive scoff before Goku could begin to answer. 

"Don't even think about it, imbecile!" he bellowed. "Trunks has enough power in his little finger to tear your pathetic body limb from limb a hundred times over. You'd be signing your own death warrant." 

Senku shot a sidelong glare at Vegeta, then scribbled another ruder note in the margin and grumbled a feeble protest under his breath.

Goku laughed, not unkindly. He gave Senku a friendly clap on the shoulder which nearly sent him staggering.

"I hate to say it, but Vegeta is right. Trunks is a Saiyan warrior. If you tried to fuse with him, the best thing that could happen is it wouldn't work. At worst, both of you could die!" 

Goku beamed. He gave Senku's shoulder a reassuring squeeze. Senku attempted to squirm out of Goku's grip with a pained wince.

"But fusion isn't the only way to get stronger, you know," Goku assured Senku. "I'd be happy to help you train. You may not be able to get as strong as a Saiyan, but anyone can learn to hold their own in a fight."

Senku wrenched his shoulder out of Goku's grip. He rubbed at his sore, bruised shoulder and scowled down at his notes.

"Like I already said _ten billion times,_ I'm a _scientist_. I don't want to hold my own in a fight; I want to figure out how this stuff _works._ "

He pointed his pencil eraser-first at Goku's face. Goku stared blankly at it.

"You martial artist warrior types can gauge people's power levels just by looking at them, right? Because of course it has nothing to do with height or weight or muscle mass or combat experience or anything you can _measure..._ " 

Goku nodded in agreement, having entirely failed to hear Senku's bitter biting tone. 

"So who around here is the same power level as me? I'll figure something out."

Goku surveyed the scene. Vegeta was still there, of course, training on his own in a quiet corner. A few of the Team Alpha combatants were in the area as well, chatting or eating or playing games. Even the shopkeepers and desk workers were more combat-ready than Senku. Jump Force didn't make room for anyone who wasn't going to be able to hold their own, except...

"Oh, that guy. The other brainiac," Goku said.

Goku pointed toward the staircase leading back to the central Jump Force hub. None other than Light Yagami descended into view, already checking his watch and politely avoiding as much eye contact as possible. Senku looked up, finally, at Light.

The paper notebook in his hands crinkled and tore in his white-knuckled grip. He grit his teeth hard. With a strangled scream in the back of his throat, Senku threw his notes into the dirt.

"Why is he so _tall?!_ " he lamented.

Light paused at the base of the stairs. His mild expression twisted in disgust and exasperation for a moment. He rolled his eyes with violent force. He ran a hand through his hair; by the time his hand was back at his side, he had a mild polite smile on his face, his perfect composure in place as if nothing had happened. He raised his voice to be heard across the clearing without having to approach.

"Can I help you, Ishigami-kun?" he asked.

Senku knelt down to pick up his notes. He brushed the dust off the pages with his fingers as he stood back up, then marched over to Light, who heroically did not grimace, flinch away, or leave. Senku held his free hand up to the top of his head, then moved it in a flat line out toward Light. Even by crude approximation, they were by no measure about the same height.

"Any chance you can shrink about ten centimeters?" Senku asked.

"I'm afraid not," Light responded. "Sorry about that."

Senku clicked his tongue irritably. He put his hands on his hips. The notes in his hand crumpled into unreadability against his coat, which he would have minded more if he had gotten anything worthwhile out of Goku earlier. He glared over his shoulder at Goku.

"Hey! Goku! How much leeway is there on this 'about the same height' stuff?!"

Goku cocked his head to the side. He looked out at a point in the distance somewhere past Light and Senku, frowning.

"...You know, the Metamorans never told me. They just said 'about the same,'" he said.

He gazed across the clearing at Vegeta. When Vegeta shot him a hostile glare, he approached. Goku towered over Vegeta, grinning.

"Now that you mention it..." he began.

"Kakarot, if you speak one word about—"

"...Vegeta and I have fused before, and Vegeta's itty-bitty!" Goku finished.

He reached out a hand to ruffle Vegeta's hair. Vegeta smacked it away before it came close. He snarled up at Goku, his fists clenching in fury. He threw a punch at Goku's stomach with crushing force. His fist made contact, but Goku shrugged it off with little more reaction than a challenging smirk.

Senku watched the exchange in silence, the gears in his head turning. He looked up at Light, then down at Goku and Vegeta. They were lowering themselves into fighting stances, so the height difference was becoming impossible to estimate a glance, but Senku knew for a fact that Vegeta was almost a head shorter. A realization came to him, and with it, the irritation melted away like ice on a hot summer day.

Senku broke away from Light, who privately breathed a sigh of relief, and approached Goku and Vegeta with a hand held up, palm out.

"Time out! Stop having this stupid fight! I have a question!"

Vegeta and Goku paused mid-battle to glare at Senku. 

"What is it?!" they snapped.

Senku smirked at them, easy confidence radiating off him in waves.

"How big are Metamorans?"

Goku's brow furrowed. He shifted out of his defensive stance to mull over the question. Vegeta took advantage of the moment of weakness to send Goku flying with a kick. Goku slammed into the far cliff wall while Vegeta cackled.

Senku shoulders slumped. The exasperation returned at full force and contorted his expression into an ugly grimace. 

"Do you have ears, old man?" he seethed. "Goku has a question to answer!"

Vegeta turned to Senku with a smug victorious smirk. He crossed his arms over his chest and tilted his head back to look down his nose at Senku despite his inferior height.

"You don't need answers from a weakling like Kakarot. _I'll_ answer your question. The Metamorans are a race of giants, each adult standing at a height of well over ten meters."

Senku threw his hands up in the air. His crumpled notebook went flying and fell to the dirt with a thud.

"Someone could have mentioned earlier! You didn't think that was _relevant?_ "

Vegeta let out a bark of laughter, then went flying out of view. Goku appeared in his place as the dust settled, with a broad grin on his face.

"Let your guard down, Vegeta!" he teased.

Within seconds, the battle was raging again. Senku picked his notebook out of the dust again and retreated back to the staircase, muttering under his breath about stupid Saiyans and their stupid bloodlust. Light was still waiting at the bottom of the stairs, watching the ongoing battle with polite feigned interest. Senku stood in front of Light and looked up at him expectantly. Light responded to what he hoped was Senku's unspoken question.

"I had business with Team Alpha, but it looks like their leader is... occupied."

Senku's unspoken question was, of course, not that one. 

"The Saiyans have a technique back home—well, they didn't invent it, but Goku's the expert we've got here—where two people can turn into one. The person that comes out is, I guess, a mix of the personalities of the people that went in, and is way stronger and faster. Sounds exciting, right? I couldn't get these idiots to explain what it feels like, if you retain your memories, if you get to _control_ any of it, so I have to try it and find out before I can figure out how to get at the mechanics, obviously."

He held out a hand to Light and put all his charm into a smirk that was half challenge, half invitation.

"So, what do you say, Light? Let's see if we can make Sento Yashigami!"

Light's polite facade cracked for a moment, revulsion and venom showing through. Senku couldn't help but flinch. In the next moment, Light's smile was back as though nothing had happened. Senku, shaken, couldn't quite bring himself to be certain Light's expression had changed at all. Surely, no one could control their facial expressions that seamlessly.

Light refused Senku's hand with what little patience he could muster. He shook his head and held up his own hand, which formed a polite but firm barrier between them.

"I'll have to pass. And I'd appreciate it if you didn't use my given name. It's inappropriate."

Senku rolled his eyes. His offer thoroughly rejected, he withdrew his hand to gesture more effectively with.

"Oh, sure. ' _Inappropriate_ ,'" he drawled. "The world is over, Light! Society's ten billion percent gone! We don't need barriers like that! We're all human beings, here!" 

Light gave Senku a slow once-over. With every new feature his eyes reached, from the hair to the scarred face to the exaggerated expression on that face to the tattered crudely-fashioned coat to the bare legs, a bit of Light's goodwill and social grace left him.

" _Your_ society may be gone, Ishigami-kun, but mine isn't," Light said flatly. He added, burying his childish spite under a thick layer of unassuming friendliness, "If you want people to take you seriously, I'd suggest you start by putting on some pants."

Senku looked down at himself and at his coat, which was the only thing he had on besides his shoes, which he had made himself, which felt like a second skin by now, then looked up. His amusement beat out his offense and settled on his face in the form of a playful smirk.

"You know, _Light..._ if you really want to get this manners stuff through my thick skull, I bet I know someone who could do it." 

He leaned in, his smirk growing wider and toothier, and held out his hand to Light again.

" _Sento Yashigami._ "

Light took a step back, leaving the illusion of friendly conspiracy floating dead in the empty air in his wake. He looked at Senku's extended hand with undisguised distaste.

"I'm sure you would love to be Senku Yagami," he said mildly. "You might have better luck with someone your own age."

Light took another look at the raging battle between Goku and Vegeta behind Senku. It showed no signs of coming to a close. Light heaved a weary sigh, turned around, and left without another word.

Senku bristled, his shoulders rising up around his ears.

"You're no fun, Light!" he hollered at Light's retreating back. "You're blocking the progress of scientific discovery! History will be on my side!"

Light did not so much as slow his ascent. Senku wrinkled his nose, straightened out his ruined notebook as best as he could, and scribbled out the details of today's spectacularly failed experiment while the Saiyans screamed and fought in the distance.

**Notes for the Chapter:**

> (A small excerpt of) Senku's notes:  
> Saiyans are aliens, but they can interbreed with humans no problem. Was there a recent common ancestor? They've got furry tails in theory, but cutting off the tails is apparently no big deal.  
> If their tails are attached, they become huge apes (really? even though they have tails? they insist they're apes and not monkeys but I don't believe it) when they see the full moon. Like werewolves.  
> If you train in marital arts, you can learn to fly in their universe, even if you're just human. No one has been able to explain to me how this works. I don't even know what I'd be trying to measure if I wanted to figure it out.  
> There's something called a 'power level' that determines... your combat ability, or something? Some of these guys can take a punch that can go right through a brick wall and come out fine, and I have no idea what's keeping their organs intact.  
> Saiyans love fighting. My sample size of two is statistically insignificant, but these guys cannot for the life of them think or talk about anything else. I'd believe it's biological.  
> Where these guys are from, two people can combine into one person that shares physical and psychological traits with both of the fused people, but is way more powerful. The fusions name is a mashup of the people who fused for some reason. Even Trunks seems pretty unclear on how this works or how it feels to do it. Maybe it messes with your memory to have to share it?  
> In order to fuse, you either need a special set of earrings ("Potara Earrings," and no one has spares) or do a Metamoran Fusion Dance, which is literally a dance. In order for the dance to work, both participants have to be the same height and the same power level.  
> Metamorans are huge, it turns out, so in human terms the height restriction is looser than you'd think.  
> No more specific information on fusion is available at the moment, because Saiyans are stupid and Light Yagami is a huge condescending dick. Experiment failed.  
> I bet Sento Yashigami (Raiku Iyagami? Light Ishigami? definitely not Senku Yagami) sucks, anyway!


End file.
